I bought a new 350x19 Dunlop K70 today at Vintage Tyres of Beaulieu for the front of my WM20. I mentioned to them that I thought the wear occurring on my last K70 that is on the rear of my WM20 seemed a bit more rapid than I was used to. After I explained the wear pattern, they suggested I was running at too high a pressure. Currently I am running at about 30 psi rear 28 psi front. Could others please comment about their tyre pressures on these soft wall modern tyres please? Ron

email (option): ronpier@talk21.com

That's about what I put in Indian Dunlops, Ron. Did you tell them that you're running big-bore and twice the catalogue horse power ?

For what it's worth on my M33 ridged with girders I run 25 front that's on a 3.25 ribbed and 30 rear on a 3.50.

My BSA rigids are run at 18 to 20lb which i think is higher than the recommended pressure.
High pressures increase the risk of the back "hopping" on a fast bumpy bend.

Same as Fred I run 18 fr 20 r in avon SM's, I was going to post about tyre life as my last front is on the limit after 5000 miles / 10 months.

Cheers Pat

My Norton steers like a BSA if it's only got 20 psi in the tyres.

I'm pretty sure the tyre companies have rationalised (reduced) the number of compounds they make..In other words K70s and SMs etc. are being made with similar (softer) compounds to the bottom end sports tyres...It's the only explanation for the shorter life of the tyres currently. I've always run the same pressures, yet the durability of the tyres has decreased noticably...
Of course the days of falling off every times it rains like you used to with the old 'slipmasters' have gone as well, so maybe it's a good thing....
As far as the correct pressure for the K70s goes the only sure way is to contact Dunlop Customer Services and ask them...
Years ago when I put track compound tyres on my Harris Matchless I contacted Avon for recommended rim sizes and built the wheels with that information. When I went to the local bike tyre center to have the tyres fitted they said they wouldn't fit them as the rim and tyre sizes weren't compatible...
Go to the manufacturer and you can be sure the information is correct...Ian

email (option): ian@wright52.plus.com

Well actually the front has a slow puncture and after two months has been as low as 12 psi which don't look flat but tends to follow the ruts.
As for the handling people said M20 watch out on bumpy bends etc but it just goes where it's pointed, but could use more clearance under the pegs.

Cheers Pat

OK I've emailed Dunlop's technical div for their comments. Be interesting to see what they say.
Ian tells me that he gets no more than about 6000 miles from a K70. Which is a lot less than I've had from Chen Shing or Mitas. But if it give better grip then I'm happy to except the more rapid wear. But still nice to know the recommended pressures. Ron

email (option): ronpier@talk21.com

I agree Ron..I based my pressures on the fact the K70 doesn't seem to have a very strong 'wall' structure..so more internal pressure tightens up the handling. This is my only real crticism of the K70, when you get a puncture it immediately 'collapses' to absolutely flat....Certainly when the bike is loaded with all my camping gear etc. it handles better with more air..Without a load I run out of clearance before any grip problems are apparent...Ian

email (option): ian@wright52.plus.com

i put 32lbs in the rear of my M20 because of my weight i also find if you let the pressure in the front tyre go to low the bike tends to wander following the contures of the road more

email (option): roger.beck@node6.com

I have found that my G3L is happiest at 18 psi front and 20 psi rear ..maybe 22 fully laden i now run a 3.50 rear tyre on the wider rim.. 3.23 front..thats on K70,s

i have noticed all tyre Manufactures including car tyres types are using softer compounds nowasdays so they wear out quicker and you need to replace more often...funny that something to do with "profits "

In my 1950 Dunlop " the Care of Motorcycle Tyres " book it gives a table of pressures against load...you need to put your rear wheel on a weighbridge or use 2 bathroom scales with a piece of wood across and add the weights together...

Left hand column psi,,next to it tyre load...

Based on 3.50 tyre Psi weight (lbs )
16 280
18 320
20 350
24 400
28 450
32 500

seems some of you like to have bumpy ride at those high pressures you are using. !!! or is it those M20,s are really that heavy !!!!

Ed Abbott

email (option): edd@abbottracing.com

I'm open to all suggestions Ed. But wouldn't your 1950 book be based on more old fashioned harder rubber? I'll see what Dunlop say, although I am inclined to do a trial at lower pressures. I recon my M20 with fuel, tools and rider is aproching 600lbs.(272kg). What pressures would you start with? Ron

email (option): ronpier@talk21.com

I don't think that it's so much the hardness of the rubber as the stiffness of the sidewall construction that is significant. What we don't really know is whether the recently produced 100% aspect ratio old style tyres have a modern more flexible sidewall construction.

The tyre loads in the period table would normally be based upon the loading on each wheel. Would the M20 be about 40% / 60% ? Probably no more than 350lbs on the rear wheel?

I certainly remember my tyre man back in the 1980s saying that the tyre pressures for TT100s given in the 1970s documentation should be increased as the sidewall construction had altered. It's therefore not a new thing with some tyres and probably reflects the final development of cross-ply tyres before radials came on the scene.

Ron

Its no so much about the rubber compound,,ie tread compound ..its more about the sidewall construction. The K70 3.50x 19 is 4 plys of Nylon which is about twice as strong as WW2 tyres...
It is also rated at 500 lbs at 33 psi..

your bike at 600 lbs will be virtually 200 lbs front 400 lbs rear..

I seem to remember my M20 was happy at 20 psi front...24psi rear no panniers ..just me..

When i last weighed a M20 with NO fuel or tools it weighed 175 lbs front
240 lbs rear. i always reckon a M20 gassed up with tools.panniers etc is sitting at 440 lbs..


Tyre safety is based on load and speed factors...speed is not going to come into the equation on WD bikes...on modern tyres so its down to weight and personel preferences....i always run mine as low as possible to get a good ride and still get good handling.. its a case of experimenting.
Before...setting off to Normandy or Holland fully laden i will raise the rear by 4 psi.

In the 1970,s Jaguar gave 5 different tyre pressure to use in the handbook dependiong on what you were doing...with a difference front to rear.
nowadays Manufactures give virtually one high setting..same front to rear ( to stop people getting confused ) because a high setting lasts longer ie as its takes longer to deflate as no one ever checks tyre pressurs anymore between services..
Manufactures and tyre companies will always want you to use a higher pressure to cover themselves...

Ed

email (option): edd@abbottracing.com

"...as no one ever checks tyre pressurs anymore between services.."

That reminds me, years ago I used to make a little extra spending money by working on people's cars at my house--mostly small to medium repairs that they couldn't do themselves.

Whenever I finished a job, I would take it out on the nearby country road for a test drive to the local station to top off the tires, even if it was just a small electrical job, like replacing headlights, etc.

Then I would just quietly smile to myself as people (mostly girls in my memory!) would say things like: "Thanks for replacing the alternator [or some other non-suspension, non-drive-affecting piece], my car runs and drives so much smoother now!"

I think that got me more additional work from others than anything else I did... all because people never check the pressures anymore... now I'm a little obsessive about always making sure my tires are at the recommended pressures.

PS: 'tires' in the US are almost exactly the same as 'tyres' in your part of the world.

email (option): nicktog@mail.com

I run 24psi front 26psi back, higher pressures make for to rough a ride with the WM20 frame,the trouble I find with the lower pressures eg 18psi it does`nt take much lose of air to drop around 14/15 psi so you have to check before every ride,I believe you need to run higher pressure in the modern tyres than older one`s,of cause if you run on a lot of dirt/sand the 18psi is proberly the way to go.

If I run 'low' pressures (K70s) with a full load on the M20 the ride is more exciting than I would like..Most of the time I run approx. 25-27 psi front and 29-31 rear...Loaded I run at 29psi front and 33-34 psi rear..Considerably higher than most people here it seems. As I noted in a previous post if you get a puncture in a K70 the fully deflated tyre just leaves the bike sitting on the rim, there seems to be no particular rigidity of the side walls...It will be interesting to see what Dunlops recommendations are when they reply to Ron's query...Ian

email (option): ian@wright52.plus.com

As most of these tyres are made in the southern hemisphere, shouldn't they be placed on with the rotation in the wrong direction to compensate???

email (option): davmax@ntlworld.com

I run my Matchless G3 at 24 PSI on the front and 28 on the back and I don't have any problem with unsound foreign compounds as they are 1950s WD vintage tyres and tubes. I keep toying with changing them for new ones, but I've never had any problems with them. They are supple, no cracks, grip well in any weather, rain, ice or snow and just don't seem to wear like modern tyres.

Sold...I'll take a pair.. ...Ian

email (option): ian@wright52.plus.com

I think Dunlops will recommend around 28psi front 32psi back & this is what I use on my 1961 Matchless G80TCS with better suspension,But I go to the lower pressures [24psi/f - 26psi/r] on the WM20 for a softer ride

I have a ribbed speedmaster on the front and it runs best in the 16 to 20 range.
the rear is a Dunlop TT 100 ( Japanese ) and it runs best 18 to 25.
the important thing is that I keep a differential of 4 to 6 between the front & back.
I get about 20 to 25 K out of a front & 10 to 15 K from the back.

Which reminds me time for a new rear.

The same tyres made in different countries usually have different compounds to suit the local conditions.
The classic racers down here used to get Irish or French tyres to race on as the compounds are a lot softer and sticker than the locally available ones

email (option): wariron@tpg.com.au

Well I just had a phone call from a nice man at Dunlop. He said they haven't done any testing of these tyres and that they would always highly recommend that you follow BSA's tyre pressures. I asked him about the soft wall issue of the modern tyre compound, to which he replied that it makes no difference as they are still cross ply tyres.
The stated tyre pressures for an M20 in my book are, 19F 28R. So not much different at the back but significantly lower at the front to what I have been running at. I'll try it on my next outing.

He also went on to say, that no official body or company would want to state in writing any deviation from the vehicle manufacturers settings as in an accident they might get blamed.

Ron

email (option): ronpier@talk21.com

As well as the 'theoretical' correct pressure the 'feel' comes into play as well...This is always the case when discussing tyres. Whether it's grip or pressures what feels 'right' to one person doesn't necessarily feel 'right' to another and it's very subjective....It always comes down to what you feel confident with...and if that's a Chinese tyre running at 5psi, a set of Avon track compounds at the right pressure won't change anything....Ian

email (option): ian@wright52.plus.com

Sounds like the usual cop out when it comes to tyre pressure,I`ll be sticking to 24psi/f 26psi/r

Dunlop Tyres are full of hot air then.. ...A complete waste of time and no help at all really..It makes you think they might as well save some money and sack the customer services department..As usual and in common with many other companies they can only help you if they can press a button and find it on their database... ..Ian

email (option): ian@wright52.plus.com

Dunlop's current stated policy does not tie in with how they operated in the past and I am not convinced that they haven't made internal constructional changes to the sidewalls and carcass since production of the K70 began.

I'm a bit of a newcomer to rigids but I have been retaining documentation since I first started motorcycling and I've looked up recommended pressures for the Norton Commandos that I know best. Until more modern tyres came along, I ran an 850 Commando on 27 front / 30 rear which I'm sure was the advice of my tyre supplier at the time.

They started off recommending 26 psi front and rear for a 3.00 / 3.50 Avon ribbed / GP combination on the 415lb Commando(the Mercury 650 which weighed 398 lb ran at 25psi).

For 1972, they began to fit K81 TT100s (still cross-ply of course) and continued with the recommendation of 26psi front and rear for solo use. The weight had allegedly come down to 395lbs.

During 1973, they suddenly became coy about pressures and isnsited on referring to manuals or the tyre manufacturer. Bikes were delivered with either Avon GPs or Dunlop TT100s.

The 1974 workshop manual lists pressures for various loads and the lowest for solo use, Avons or Dunlops, is 22 front / 24 rear which rather makes a mockery of the 26psi that they were recommending the year before.

The 1975 Model year Commandos were the heavier electric start models and the recommnedations changed to 24 front / 26 rear. This was the last model of Commando produced and NVT went into receivership during 1976 so are unlikely to have made any further recommendations.

However, I have a Dunlop leaflet giving fitment and pressure across a range of machines. It is undated but includes the TT100 and the 'Red Arrow' which must date it to around 1979 / 80, I think. This lists the pressures for all Commando models, solo with 80kg rider as 28 front / 30 rear.

The pressures for all the bikes listed are in this sort of area so it isn't just a Commando thing.

To my mind, there were clearly changes made to the construction of K81s at least, during the late 1970s and that ties in with what I remember of dealer advice at the time.

Only Dunlop could say from their production record if K70s altered as well and they seem to be unable / unwilling to do so.

The 1970s was the era of ill-handling Japanese machines and an obsession with directional stability. Did they alter existing ranges to make them suitable for bikes with a hinge in the middle ?

The K70 was not of course an original fitment on the WDM20 (or probably any M20). Does anyone have any early 1960s Dunlop literature showing recommended pressures for earlier machines ?

Interesting stuff Rik..It seems to me that as Dunlop sell the K70 as a general purpose tyre and therefore suitable for a wide variety of machines they should be able and prepared to make recommendations in response to an enquiry..They, after all, should know more about their own tyres than the average consumer.
A few figures relating to the overall features of a bike should be all they would need to make such a recommendation...and if a K70 was fitted as standard to a bike then they would make a recommendation....
Imagine if companies sold pistons but refused to give you a clearance figure..that would be considered absurd..likewise with Dunlop... ...Ian

email (option): ian@wright52.plus.com

I find it strange, Ian.

As far as I can tell, the K70 is likely to have differed from the original tyres when it was introduced in the 1960s so pressures even then were probably a little higher than the factory manuals. Unfortunately, I can't find any 1960s literature to check.

I can't believe that Dunlop would encourage me to run at the pressures detailed in the Norton manuals for 3.25 tyres - 17psi front, 20psi rear !

I wonder if Avon's technical department would be more helpful (they still make Speedmasters from the same era).

K70s were standard equipment on T140s up until the late 1970s. I wonder if the recommendations changed over that period ? *

* I've found an on-line Triumph manual which infers that they stayed at 24/24 all the time the K70s were fitted as original (1977 or so ?) but that when they later fitted K81s, this was at 28/32. The question remains, did just the K81s change construction or the K70s as well...and are modern K70s the same as originals ? That they are of a softer compound means that they will warm up more and should need higher pressures to prevent overheating but this would be at the cost of comfort. Can a sv overheat its tyres ?

Probably...it can overheat everything else.. ..On that subject how is the Norton running? I guess you havent been riding around too much in the currect weather...it's minus 4 here at the moment..but how many miles have you got on it since the work was done?....Ian

email (option): ian@wright52.plus.com

Ian, it's been down to -14°c here and snowed till lunchtime. I had a fiddle around in the garage and wondered if I could magically transport a bike to somewhere warm....

The 16H seems to have been behaving itself but I can't remember what the mileage was back in May. I probably haven't ridden as far as it felt like on my over-inflated tyres...

Hi all,interesting comments ,for wat its worth i,ll chuck my 2 bobs worth in, i run my k70,s at 18 & 20 ,I,m only a lightweight and most of my roads ,well mainly offroads,Like the handling and bit more forgiving in the potholes works for me.Was very surprised at the dunlop response,have to wonder if your dealing with a foreign call center.

email (option): cruiser3@icisp.net.au

End of the month I will be buying the tyres for my 1945 M20.
I want the Dunlop K70's but I thought that the recommended tyres were 325 front and back, heard recommendations for a 350 on a rear but not the front?
Why have you got a 350 on the front Ron?

email (option): 79Aust@sky.com

Julian, it's just a case of getting a bit more rubber on the road. Plus, it makes it easier to line up the wheels with a straight edge if they are the same size.

Ron

email (option): ronpier@talk21.com

I run my M20 tyres (Mitas rear and an ancient Speedway front) fairly low at around 18 to 22 psi. But then, I've kept my youthful and boyish figure unlike some of you more "comfortable" riders. But as daft as it sounds, it seems that different days require different pressures (as much as 5-8psi).

The ambient temperature no doubt plays a small factor by expanding the air in the tyres, but maybe that's counteracted by the slightly softer sidewalls (collapsing in the heat). Can't be much in it, either way. Nevertheless, I have to adjust the pressures fairly often before I'm satisfied (maybe we have thicker air in London).



But more worryingly these days are the state of the (UK) roads. In my neck on the woods, there are asphalt craters like foxholes. Hit one of those unexpectedly while your pressures are down, and you'll quickly wreck your rims, and maybe much more.

Consequently, I'll be looking for a little more bounce for the foreseeable future. And the roads will get a lot worse before they get better. The street outside my home has, in places, lost a couple of layers of tarmac and is now down to the 100-year old stone setts. There's a hole at the end that must be ten inches deep.

Factor that in everyone.

email (option): dannydefazio@sumpmagazine.com

Thanks Ron,
I will need to re-align all as it has been completely re- built so glad you recommended the same front and rears.
350's it is I think as the 325's do look a bit skinny.

email (option): 79Aust@sky.com

british roads i am thinking of wearing a gum sheild i have hit hole that would shake your teeth out

email (option): roger.beck@node6.com